A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
An embodiment of a lithographic apparatus may exploit a liquid supply system to provide liquid (i.e., an immersion liquid) on a localized area of the substrate and in between a final element of the projection system of the lithographic projection apparatus and the substrate. The liquid supply system has a liquid confinement system so as to confine the liquid between the final element of the projection system and the substrate, the substrate generally having a larger surface area than the final element of the projection system. The liquid is, e.g., distilled water. However, another fluid may be suitable, particularly a wetting fluid, an incompressible fluid and/or a fluid with higher refractive index than air, desirably a higher refractive index than water. Fluids excluding gases are particularly desirable. The point of this is to enable imaging of smaller features since the exposure radiation will have a shorter wavelength in the liquid than in air. The effect of the liquid may also be regarded as increasing the effective numerical aperture (NA) of the projection system and also increasing the depth of focus. Other immersion liquids have been proposed, including water with solid particles (e.g., quartz) suspended therein, or a liquid with a nano-particle suspension (e.g., particles with a maximum dimension of up to 10 nm). The suspended particles may or may not have a similar or the same refractive index as the liquid in which they are suspended. Other liquids which may be suitable include a hydrocarbon, such as an aromatic, a fluorohydrocarbon, and/or an aqueous solution.
A lithographic apparatus may comprise one or more tables (also referred to as stages). For example, the lithographic apparatus comprises a first substrate table for accommodating a first substrate, and a second substrate table for accommodating a second substrate. The first substrate on the first substrate table is being subjected to an exposure (or: imaging) operation via the projection system, while the second substrate on the second substrate table is being subjected to a measuring operation prior to being subjected to the exposure operation. As another example, the lithographic apparatus comprises a first table (i.e., a substrate table) for accommodating a substrate, and a second table (i.e., a measurement table) for accommodating measurement instruments for performing various measurements related to the exposure operation.
In an embodiment of a lithographic apparatus, which exploits a liquid supply system of the kind addressed above, and in which two (or more) tables or stages are provided, the liquid confinement system may use the upper surfaces of the two or more tables (i.e., the surfaces of the tables oriented substantially perpendicularly to an optical axis of the projection system and facing a direction opposite to a main direction of the exposure radiation in the projection system) and/or use the substrate accommodated at a specific one of the tables as a functional component in order to confine the immersion liquid.
A lithographic apparatus is known from U.S. Pat. No. 7,310,132 B1, incorporated in its entirety herein by reference. In U.S. Pat. No. 7,310,132 a lithographic apparatus is described including two substrate tables. Each substrate table is provided with a long stroke module and a short stroke module which forms part of the second positioner for moving the substrate. Furthermore, the known lithographic apparatus is provided with a swap bridge in the form of a movable member. U.S. Pat. No. 7,310,132 B1 describes two main embodiments of the known lithographic apparatus. In a first configuration the substrate tables are movable with respect to each other, and in a second configuration, the substrate tables are coupled via the swap bridge which is realized by bringing the top surfaces of the substrate stages together by using the movable member for a joint movement. Another movable member is disclosed in US 2010/0128241, incorporated in its entirety herein by reference.